Copying system, method and components

ABSTRACT

An electrophotographic (or magnegraphic) copying system is disclosed which employs a doner sheet bearing toner particles adhered by electrostatic charge on one or both surfaces thereof, a photoresponsive member having a copy surface on which a charge image is formed, and electrically insulating liquid for application to the imaged surface whereby toner particles migrate from the doner sheet to the copy surface for fixing thereon.

United States Patent 1191 Anderson 1451 Sept. 2, 1975 COPYING SYSTEM,METHOD AND COMPONENTS [75] Inventor: Terry G. Anderson, Pasadena, Calif.

[73] Assignee: Bell & Howell Company, Pasadena,

Calif.

[22] Filed: Jan. 30, 1974 [21] Appl. No.: 438,102

Related US. Application Data [62] Division of Ser. No. 323,165, Jan. 12,1973.

[52] US. Cl. 355/3 DD; 355/16; 117/17.5; 117/37 LE; 96/1 SD; 118/637[51] Int. C1. G03G 15/00 [58] Field of Search 355/3 R, 3 DD, 16; 117/37,l17/17.5; 96/1 SD; 118/637 [56] References Cited UNITED STATES PATENTS2,837,441 6/1958 Kaiser ll7/l7,5 3,166,432 l/1965 Grindlach 3,245,8234/1966 Mayo ll7/l7.5

3,247,007 4/1966 Oliphant 1 117/37 3,375,806 4/1968 Nost 355/3 DD3,592,678 7/1971 Honjo et a1. 117/37 FOREIGN PATENTS OR APPLICATIONS790,013 7/1968 Canada 117/37 Primary Examiner-Richard M. Sheer Attorney,Agent, or FirmNilss0n, Robbins, Bissell, Dalgarn & Berliner [57]ABSTRACT 3,232,190 2/1966 Willmont 355 3 DD 9 Claims, 3 Drawing Figures25 :51 42 1.] 68 v 24 44 a9 -36 64 66 N 6 1 2O (17( 6 52 2 1 16/ )1 /8'[if 11 ll 69 -62 /2: D u /4 4/ r T COPYING SYSTEM, METHOD AND COMPONENTSThis is a division of application Ser. No. 323,165, filed Jan. 12, 1973.

FIELD OF THE INVENTION The present invention generally relates tocopying and more particularly to an improved method and system forelectrophotographie and magnegraphic copying.

BACKGROUND AND SUMMARY OF THE INVENTION There are currently severalwidely used charge copying systems. In electrophotographic systemsemploying a dry development method, dry toner particles normally arepassed into contact with an electrostatically imaged photoconductivesurface to form the desired visible image. Problems often arise duringcontinual use of the copying machine. Thus, dry, finely particulatetoner particles can spread throughout the body of the machine and mayinterfere with the production of clean crisp copies. Cleaning of themachine may have to be carried out periodically to reduce such problems.Moreover, untidy replacement of the dry toner also has to be carried outperiodically.

Other systems use magnegraphic principles to form a (magnetically)charged image and utilize magnetically attractable toner particles forproviding copies. The foregoing considerations are similarly applicable.

Although liquid development systems avoid the airborne spread of drytoner particles, they are also subject to certain disadvantagesincluding the possibility of spillage and the need for substantial spacewithin which to accommodate a storage tank, agitator, pump, applicatorand recovery means for excess liquid toner. They are not sufficientlycompact to be used in small spaces and, because of their multigude ofcomponents, are usually expensive.

Accordingly, it would be desirable to provide an improved charge(electrographic or magnegraphic) copying system which would be compactand inexpensive and which would avoid airborne contamination prob lemsof dry toner systems as well as the disadvantages of most liquiddeveloping systems. It would also be desirable for such a system to beusable as a home copying system, that is, it should neither requirecomplicated procedures nor training in its use nor the use of elaborateequipment.

The present invention satisfies the foregoing needs and provides animproved charge copying system and method as well as an improved donercartridge for the same and a novel method of fabricating a doner sheetfor use in the system and method. In particular, the improved method andsystem employ a doner sheet capable of holding an electrostatic chargeand bearing toner particles on one or more surfaces thereof, aphotoconductive copy surface, means for charging the copy surface andforming a charge image thereon, an electrically insulating liquid forapplication to the imaged sur face and stripping of the toner particlesfrom the doner sheet on contact. means for applying the liquid and meansfor fixing the toner particles on the copy surface. The doner sheet,copy sheet and liquid can be separately stored, the liquid being appliedimmediately before the contact with the doner sheet. The donor sheet canbe fabricated by electrostatically charging one or both sides of aninsulating sheet and then uniformly developing with charged tonerparticles which adhere by electrostatic attraction. An externalelectrical field can be applied to facilitate migration of tonerparticles from the donor sheet through the insulating liquid to theimage copy surface. By appropriate application of the external field,reversal copying can readily be carried out.

The present system is compact, inexpensive and requires no specialskilled or complicated techniques, Accordingly, it is ideal for a lowcost, efficient home copying unit. It avoids the problems inherent inconventional dry toner systems and in liquid developer systems. Thedepletable components of the system can be packaged in a cartridge foreasy removal and replacement. Moreover, such components can be easilyfabricated of conventional, readily available materials. Clear, crisp,accurate copies of original negatives or positives can'be provided.Other advantages are set forth in the following detailed description andaccompanying drawings,

For purposes of simplicity of presentation the discussion hereinafterwill refer to electrophotographic systems, but the considerations,insofar as attraction of toner particles, also apply to magnegraphicsystems, toner compositions for which are well known to the art. Whenthe term charge" is used, in the claims and specification, it is meantto refer to both electrostatic charge and magnetic charge (or field).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically depicts oneembodiment of the electrophotographic copying system of the presentinvention;

FIG. 2 schematically depicts in greatly enlarged form the transfer oftoner particles from a donor sheet to an electrostatically imaged copysheet in accordance with the present method and system; and

FIG. 3 schematically depicts in side elevation one embodiment of thedonor cartridge of the invention, portions being broken away toillustrate internal features thereof and portions being shown in dottedoutline.

DETAILED DESCRIPTION The present method of electrophotographic copyingcomprises electrostatically charging a photoconductive copy surface,exposing the charged surface to a light pattern to form a latentelectrostatic image thereon, coating the image surface with a layer ofan electrically insulating liquid capable of wetting the surface,contacting the layer with a donor surface bearing toner particles,causing the toner particles in the charged state to migrate through theinsulating liquid to the imaged surface, after which the resultingvisible image is fixed either by drying or by heating to provide apermanent copy.

Referring particularly to FIG. 1, one embodiment of the system of thepresent invention is schematically depicted. An electrophotographicsystem 10 is shown which includes a photoconductive surface in the formof or on a sheet 12 of appropriate length disposed in a cartridgecompartment 14. The photoconductive sheet 12 is moved from thecompartment 14 by suitable means, such as a movable (by mechanism notshown) feed roller 16 and passes through suitable guide means such asguide rollers 18, 20, 22 and 23. It will be understood that the sheet 12can be relatively short and a plurality thereof can be stored in stackedrelation in the compartment 14. In that event, transparent means such asa moving belt or web (not shown) can be used to pass each sheet 12through system 10.

The sheet 12 can be fabricated of any conventional electrostaticallychargeable photoconductive material, such as zinc oxide disposed in aninsulating binder as a coating on a paper sheet or the like. It will beunderstood that other suitable photoconductors can be used in place ofzinc oxide, for example, zinc sulfide, cadmium sulfide, vitreousselenium, zinc silicate, anthracene, triphenylamine, polyvinylcarbazole, and the like. The binder can be any conventional electricallyinsulating binder, for example, silicone, polyester, vinyl copolymers,phenolic resin, epoxy resin, polyurethanes, phenolic resins, acrylicresins and the like. The supporting sheet, if any, for thephotoconductive coating can be paper, plastic, metal foil, or the like,all within the skill of the art As the sheet 12 passes between the guiderollers and 22 it is electrostatically charged by a unit 24, which canbe any suitable conventional charging unit, for example, a standardcorona device well known in the art for such purposes. The sheet 12, nowhaving an electrostatically charged surface 11, is passed to an exposurestation wherein the charged surface 11 is exposed to a light patternformed in any suitable conventional manner such as by interposing anegative or positive original 26 between a light source 28 and sheet 12.The electrostatic charges on the photoconductive surface 11 aredischarged in those areas struck by light, while the remaining areas ofthe surface 11 retain their electrostatic charges. Accordingly, a latentelectrostatic image duplicating the original is formed on the surface11. The latent image 29 is depicted in FIG. 2. Well known techniques forobtaining a positive image from either a positive or negative originalcan be used.

It will be understood that the sheet 12 is kept in the dark, except forthe described exposure, until after it has been developed and fixed. Forsuch purposes, the system 10 may include an outer container 30 withmeans 32 for inserting and removing the original 26 to be copied. Thelight source 28 is on only when the exposure is to be made. Eithertransmissive or reflective optics can be used.

After the described exposure, the sheet 12, now bearing the desiredlatent electrostatic image 29 on the photoconductive surface thereof, ispassed to the developing portion of the system 10 by suitable drivemeans including the drive roller 67, referred to hereinafter. Ifdesired, the imaged sheet 12 can be provided with a substitute latentelectrostatic image which is the reverse of that produced in the mannerdescribed above. This can be accomplished by positioning the sheet 12adjacent to an electrical field generating means 34, such as a constantcurrent corona device of opposite charge with respect to the coronadevice 24. The device 34 generates an electrical field which neutralizesthe electrostatic image pattern 29 on the sheet 12 and imposes anelectrostatic charge pattern of opposite polarity on the previouslyimage-free area of the surface 11. Accordingly, if the original document26 is a negative, a positive copy can be produced by this reversaltechnique, provided that the photoconductive surface employed issuitable for such purposes and toner is selected so as to cause tonerparticles to be attracted to the substitute latent electrostatic image.Alternative methods employing a bias potential during development are1180 known to the art.

A reversal image can also be provided by eliminating the use of means 34but reversing the polarity of corona device 24 and utilizing either aconventional bichargeable photoconductive surface such as zinc oxidemixed with zinc sulfide or a photoconductive surface capable ofaccepting electrostatic charges of the opposite polarity, i.e., thoseinduced by corona device 24 or its reversed polarity mode. In thisinstance, the toner particles do not deposit out on the latentelectrostatic image but are repelled thereby (being of the samepolarity) and are deposited on the imagefree areas of thephotoconductive surface. Accordingly, there would be no need to changethe type of toner particles employed in system 10 in order to obtain apositive print.

The imaged photoconductive surface 11 of the sheet 12 is next wettedwith a suitable electrically insulating liquid 36 as illustrated in FIG.2. The liquid 36 is disposed as a layer 37 on the photoconductivesurface 11 by applicator means such as a roller 38 having a porous outersurface 40 communicating with an interior liquid storage cavity 42. Theliquid 36 need only be applied to the imaged photoconductive surface ofsheet 12 immediately before development thereof. Moreover, a layer 37 ofthe liquid 36 so applied need only be of an extent sufficient tomobilize toner particles, more particularly as described hereafter, andfacilitate their migration to imaged photoconductive surface 11. Othersuitable storage means for the liquid 36 can be used in addition to orin substitution of the roller cavity 42. The surface 40 can be of anysuitable material, such as porous plastic, porous rubber or the like.

The liquid 36 can comprise any suitable electrically insulative liquid,for example, iso-paraffins, such as sold under the trademark Isopar G byHumble Oil and Refining Co., or suitable aromatic hydrocarbons, such astoluene, xylene or the like, substituted or unsubstituted. Certainaliphatic and cycloaliphatic hydrocarbon liquids are suitable, inaddition to iso-paraffins, for example, n-pentane, benzene, cyclohexane,and the like. The liquid medium and toner are selected to provide properattraction of the toner particles to the latent electrostatic image. Theliquid 36 should be absorbable by the photoconductive sheet 12 andvolatilizable therefrom so that layer 37 thereof is readily eliminatedafter use.

Referring to FIG. 2, development of a latent electrostatic image 29 onthe photoconductive surface 11 to a visible image is achieved by passingthe sheet 12 into close proximity to a donor sheet 44 bearing a layer 46of toner particles thereon so that the liquid layer 37 contacts thetoner layer 46. Conventional dry toner particles charged with oppositepolarity to that of latent image 29 usually are utilized Such tonerparticles can be formulated with, for example, carbon black, chromeyellow, cadmium red, red or black iron oxide, Prussian blue, Hansayellow, crystal violet or other conventional colored toner particles.

The donor sheet 44 comprises a web of electrically insulative materialto which the toner particles 48 adhere by a weak electrostatic force sothat the electrostatic attraction of toner particles 48 by the latentimage 29 on the photoconductive surface ll substantially exceeds theforce binding particles 48 to the surface of sheet 44. The insulatingsheet 44 can be of any conventional composition. Thus, one could usedielectric coated paper that is chargeable to the polarity desired.Light sensitivity is not needed as the electrostatic charge will be usedonly for uniform adherence of the particles. Alternatively, one coulduse any insulating sheet material capable of carrying an electrostaticcharge, such as Mylar, Kapton, polyethylene. polypropylene, polysulfone,or the like. The surface of the donor sheet 44 is then developed bycontact with charged toner particles having an opposite polarity. Thetoner particles can be formulated with a binder, as known, and can beapplied, for example, as a liquid slurry. Preferably, the slurry liquidshould not be a solvent for the binder. The binder may be thermoplastic,e.g., polyethylene resin, in which case it need not be soluble in theinsulating liquid layer 37 and can be subsequently fixed by heating.However, any plastic, thermoplastic or otherwise, which is soluble inthe insulating liquid can be used, in which case fixing can beaccomplished by single drying and heat fixing would not be required.Alternatively, dry toner particles can be applied to the charged donorsheet surface by spraying. In any case, the toner deposited on the donorsheet 44 will not be fixed but will be transferable, as hereinafterdescribed.

Contact between the liquid layer 37 and the toner layer 46 results, asshown in FIG. 2, in the transfer of charged toner particles to theimaged photoconductive surface 11 in those areas bearing the latentimage 29. In the example illustrated in FIG. 2, the electrostatic image29 bears negative charges, while the toner particles 48 are positivelycharged. Thus, the electrostatic attraction exerted by the latent image29 on the toner particles 48 after mobilization of those particles bythe liquid layer 37 results in migration of the toner particles from thedonor sheet layer 46 to the latent image, adhering thereto and renderingit visible.

Obviously, the influence of the electrostatic attraction by the image 29after the toner mobilization must be greater than the forces binding thetoner particles to the doner surface 46. If such influence is notinitially greater, it can be made so through the use of an externalelectrical charge-generating device 50 positioned adjacent the donorsheet 44, or sheet 12 or both. The charge-generating device 50 can beused to induce as strong an electrostatic charge density in the latentimage 29 as is necessary to assure proper migration of toner particlesto the vicinity of the latent image 29.

After the toner particles deposit on the latent image 29, the resultingvisible image can be made permanent by any suitable fixing procedure. Byformulating the toner particles 48 with a thermoplastic binder, heatingof the visible image to above the melting point of the thermoplasticbinder, as by a heater 52 will fuse the binder to the photoconductivesurface 11 and permanently bond the visible image thereto on cooling.For such purposes, binders such as polyethylene, polyvinyls,polystyrene, polypropylene, acrylic resins and the like can be used,provided their melting point is below that of sheet 12 and itsphotoconductive surface 11 and is reasonably low. A particularly usefulmaterial containing toner particles formed with a thermoplastic binderis a developer sold by the Bell & Howell Co. under the trademarkStatesman.

The heater 52 also facilitates the evaporation of residual amounts ofthe liquid 36. After the fixing step, the finished copy is clear andsharp and is passed through a cutting mechanism 53, as known, and passesfrom the housing 30.

It will be understood that the photoconductive sheet 12 can be, ifdesired, a plurality of separate sheets disposed in a suitable storagearea and sequentially retrievable therefrom by any conventionaltransport and handling means. The donor sheet 44 also can be a pluralityof sheets sequentially retrievable from a separate storage area, also byconventional transport and handling means. However, it is preferred toprovide a single long donor sheet in the form illustrated moreparticularly in FIG. 3, or a long donor sheet 44 in the form of acontinuous roll (not shown). FIG. 3 schematically depicts the donorsheet 44 disposed in and as part of a donor cartridge 52. The cartridge54 includes a housing 56 defining apertures 58 and 59 in opposite,respective side walls 60 and 61. The donor sheet 44 is wound on opposedfreed and take-up spindles 62 and 63. Guide rollers 64 and 65 aredisposed within the housing 56 so that opposite surfaces of the donorsheet 44 are exposed through the respective apertures 58 and 59. Inoperation, one of the guide rollers (64 as shown) is closely spacedadjacent a drive roller 67 within the container 40 (FIG. 1) to press thedonor sheet 44 into contact with the processed sheet 12. A gearingmechanism (not shown, but indicated at 69 in FIG. 1) can connect thedrive roller 67 to the take-up spindle (62 in this case) so that thedonor sheet 44 is advanced in synchronization with the photoconductorsheet 12.

In the embodiment depicted in FIG. 3, and also in FIG. 1, when one sideof the donor sheet 44 has been exhausted, i.e., toner particles havebeen stripped from the entire length thereof, the cartridge 54 can beremoved from housing 30 and reversed so as to abut the other aperture 59against the photoconductive sheet 12 and expose the second of the twotoner-bearing sides of the donor sheet 44. The donor sheet 44 can thenbe progressively rewound as subsequent copies are developed until thesecond side is depleted of toner and replacement of the cartridge 54 isrequired.

It will be understood that the cartridge 54 can be provided with acontinuous donor sheet disposed around spindles 62 and 63 and rollers64, 65 and bearing toner particles on only one side thereof, if desired.In such event, the cartridge 54 need only contain one aperture 58.

Various modifications, changes, alterations and additions can be made inthe present electrophotographic copying method, its steps andparameters, in the method of fabricating the donor sheet, in the presentelectrophotographie system, its components and in the novel donorcartridge and its components. All such modifications, changes,alterations and additions as are within the scope of the appended claimsform part of the present invention.

1 claim:

1. An improved copying system comprising, in combination:

an elongate donor sheet of insulating material having a donor surfacebearing toner particles uniformly adhered to said surface byelectrostatic charge;

a copy member having a copy surface;

means for charging said copy surface;

means for selectively dissipating said charge to form a charge image onsaid copy surface;

storage means containing an electrically insulating liquid capable ofstripping said toner particles from said donor surface for migration tosaid chargedimaged surface;

applicator means for applying said liquid as a layer to said copysurface when said copy surface bears said charge image;

means for bringing said donor surface and said liquid layer on said copysurface into contact; and means for fixing said toner particles as apermanent visible image on said copy surface.

2. The system of claim 1 wherein said toner particles are held on saiddonor surface by forces weaker than the charge attraction afforded bysaid imaged copy surface.

3. The system of claim 2 wherein said copy member comprises at least oneelongate, flexible sheet.

4. The system of claim 3 wherein said copy member. said donor sheet andsaid insulating liquid are in separate compartments and wherein saidapplicator means is positioned to apply said liquid to said imaged copysheet immediately before contact with said donor sheet.

5. The system of claim 3 herein both sides of said donor sheet bear saidtoner particles adherent thereto and wherein said donor sheet isdisposed in a cartridge providing access to both sides of said donorsheet.

6. The system of claim 3 wherein said toner particles includethermoplastic binder transferable therewith.

7. The system of claim 3 wherein said toner particles include plasticbinder soluble in said layer of electrically insulating liquid.

8. The system ofclaim 2 wherein said system includes means for providingan external electrical field adjacent said donor surface during saidmigration to facilitate the same.

9. The system of claim 2 wherein said charge image is an electrostaticcharge image and said system includes means for providing an externalelectrical field adjacent said copy surface for reversal of said chargeimage on said copy surface.

1. An improved copying system comprising, in combination: an elongatedonor sheet of insulating material having a donor surface bearing tonerparticles uniformly adhered to said surface by electrostatic charge; acopy member having a copy surface; means for charging said copy surface;means for selectively dissipating said charge to form a charge image onsaid copy surface; storage means containing an electrically insulatingliquid capable of stripping said toner particles from said donor surfacefor migration to said charged-imaged surface; applicator means forapplying said liquid as a layer to said copy surface when said copysurface bears said charge image; means for bringing said donor surfaceand said liquid layer on said copy surface into contact; and means forfixing said toner particles as a permanent visible image on said copysurface.
 2. The system of claim 1 wherein said toner particles are heldon said donor surface by forces weaker than the charge attractionafforded by said imaged copy surface.
 3. The system of claim 2 whereinsaid copy member comprises at least one elongate, flexible sheet.
 4. Thesystem of claim 3 wherein said copy member, said donor sheet and saidinsulating liquid are in separate compartments and wherein saidapplicator means is positioned to apply said liquid to said imaged copysheet immediately before contact with said donor sheet.
 5. The system ofclaim 3 wherein both sides of said donor sheet bear said toner particlesadherent thereto and wherein said donor sheet is disposed in a cartridgeproviding access to both sides of said donor sheet.
 6. The system ofclaim 3 wherein said toner particles include thermoplastic bindertransferable therewith.
 7. The system of claim 3 wherein said tonerparticles include plastic binder soluble in said layer of electricallyinsulating liquid.
 8. The system of claim 2 wherein said system includesmeans for providing an external electrical field adjacent said donorsurface during said migration to facilitate the same.
 9. The system ofclaim 2 wherein said charge image is an electrostatic charge image andsaid system includes means for providing an external electrical fieldadjacent said copy surface for reversal of said charge image on saidcopy surface.